1. Field of the Invention
The present invention relates to a socket used for electrically connecting a semiconductor device, i.e., an Integrated Circuit (IC), to the circuit board of a testing apparatus or system and more particularly, to a socket preferably used for a surface-mounting semiconductor device that comprises electrodes arranged in the form of xe2x80x9carea arrayxe2x80x9d at the bottom of its package, in which the electrodes at the package bottom are electrically connected to the circuit board.
2. Description of the Related Art
In recent years, the need of the market to provide semiconductor devices (ICs) with multiple function, high-speed operation, and low power consumption has been becoming stronger. According to this need, the package type of semiconductor devices has been changed. Specifically, instead of the conventional Quad Flat Package (QFP) with electrodes arranged at its periphery, the xe2x80x9carea array packagexe2x80x9d with electrodes arranged at its bottom, such as the Ball Grid Array (BGA) and Land Grid Array (LGA), has been becoming popular. With the area array package, electrodes are arranged at the flat bottom of the package in the form of area array.
Generally, on testing the electrical characteristics of the IC chip encapsulated in the package, the packaged semiconductor device is electrically connected to the circuit board of a specific testing apparatus or system by way of a socket. Conventional sockets (i.e., testing sockets) have typically had the structure comprising a punched metal plate and contact pins fixed to the plate. However, to test a semiconductor device with the area array package, the conventional sockets are unable to provide satisfactory electrical characteristics. Thus, various techniques relating to the testing sockets themselves and materials used therefor have been developed and proposed so far.
For example, the Japanese Non-Examined Patent Publication No. 7-287048 published in 1995 discloses an IC socket designed for ICs with the BGA package. This socket comprises an elastic rubber plate and springy contact pins arranged on the surface of the plate two-dimensionally. However, this socket has a problem that the durability is low. Specifically, the contact pins are likely to be deformed with the increasing operation time. As a result, there is a possibility that the electrodes of the IC or semiconductor device do not contact the pins as desired, degrading the reliability.
The Japanese Non-Examined Patent Publication Nos. 9-35789 and 9-161870 published in 1997 disclose an anisotropically conductive sheet applicable to IC sockets. The sheet comprises an elastic rubber body and thin metal wires buried in the sheet, which have an advantage to provide improved contact with the semiconductor device. However, the sheet has a problem that it is unable to cope sufficiently with the miniaturization of the device and pitch narrowing of its electrodes. This is because the metal wires are arranged obliquely to the direction perpendicular to the sheet itself and as a result, it is difficult to decrease the distance between the contact points on the surface of the sheet.
The Japanese Non-Examined Patent Publication No. 5-62727 published in 1993 discloses an anisotropically conductive connection member applicable to mounting an IC chip on a circuit board or a package. This member comprises an elastic rubber sheet and bunches of metal wires buried in the sheet, where these bunches of wires are selectively provided at positions corresponding to the pads or electrodes of the IC chip and the circuit board or package. This member has an advantage that it can be used for test of IC chips with miniaturized and pitch-narrowed pads/electrodes because the wires are fixed perpendicular to the sheet itself. However, this member has the following problem.
Specifically, the bunches of wires disturb the elastic deformation of the rubber sheet and thus, the intrinsic elastic property of the sheet is damaged. Accordingly, if the member is applied to test of IC chips with the BGA package, excessive force tends to be applied to the ball-shaped terminals or electrodes of the chips. This causes a problem that the terminals/electrodes are likely to be damaged.
Moreover, the Japanese Non-Examined Patent Publication No. 11-214594 published in 1999 discloses an anisotropically conductive sheet applicable to test of IC chips. This sheet comprises an elastic rubber body and conductive particles selectively distributed in the sheet at positions corresponding to the pads or electrodes of the IC chip and the circuit board for test. This sheet has an advantage that it can be used for test of area-array packaged IC chips with miniaturized and pitch-narrowed pads/electrodes.
The Japanese Non-Examined Patent Publication No. 10-197599 published in 1998 discloses a test apparatus of semiconductor devices or ICs. This apparatus comprises an anisotropically conductive sheet and an insulating sheet. The insulating sheet has openings at positions corresponding to the pads or electrodes of the IC chip to be tested. In the testing operation, the insulating sheet is placed between the anisotropically conductive sheet and the IC chip in such a way that the pads/electrodes of the chip are engaged with the openings of the insulating sheet, improving the positioning accuracy of the chip. This apparatus can be used for test of area-array packaged IC chips with miniaturized and pitch-narrowed pads/electrodes.
An example of the conventional IC sockets of this type is shown in FIG. 1, in which the use of the IC socket is illustrated.
As seen from FIG. 1, the conventional IC socket 210 comprises an anisotropically conductive sheet 208 and a frame-shaped package guide 207 surrounding the periphery of the sheet 208. The sheet 208 is formed by an approximately rectangular, sheet-shaped base material (i.e., body) 204 and conductive particles 203 distributed locally therein. The base material or body) 204 is made of an insulating, elastic rubber. The particles 203 are selectively provided at positions corresponding to the electrodes 206 of a circuit board 205 of a test apparatus (not shown) and the solder balls 201 of a semiconductor device, i.e., IC chip 200, to be tested. As the base material 204, silicone rubber or the like may be used. The average diameter of the particles 203 is, for example, several tens micrometers (e.g., 40 xcexcm).
The package guide 207, which is made of an insulating material, has the same approximately rectangular plan shape as the sheet 208. The size of the guide 207 is so designed that the body 202 of the IC chip 200 is fitted into the guide 207, as shown in FIG. 1.
When the IC chip 202 is subjected to a test on the test apparatus, the chip 202 is electrically connected to the circuit board 205 by way of the anisotropically conductive sheet 208. Specifically, first, the chip 202 is inserted into the guide 207 so that the solder balls 201 are placed on the respective conductive regions (in which the conductive particles are distributed) of the sheet 208, as shown in FIG. 1. Next, a downward pressure is applied to the body 202 of the chip 200, thereby pressing the balls 201 toward the sheet 208 and causing deformation of the conductive regions of the sheet 208. Because of the deformation of the regions, the conductive particles 203 existing in the regions are contacted with each other, forming electrical paths between the balls 201 of the chip 200 and the electrodes 206 of the board 205. As a result, the balls 201 are electrically connected to the corresponding electrodes 206.
Typically, to confirm the position of the bottom ends of the solder balls 201, the bottom ends of the balls 201 may be monitored or checked with a suitable sensor in the test operation. From this point of view, it is necessary that the surfaces of the balls 201 include no or less damages and solder waste.
The conventional IC socket 210 shown in FIG. 1 has an advantage that the solder balls 201 are difficult to be damaged. However, it has the following three problems.
The first problem is that it is difficult to make sure the electrical connection of the chip 200 to the board 205.
Specifically, with the anisotropically conductive sheet 208 of the IC socket 210, the average diameter of the conductive particles 203 is small and thus, the adjoining particles 203 are difficult to contact with each other. Therefore, if the deformation of the base material or rubber 204 of the sheet 208 is insufficient, the electrical resistance in the conductive regions of the sheet 208 does not decrease as desired. This means that desired electrical paths are not formed between the solder balls 201 of the chip 200 and the electrodes 206 of the board 205. As a result, there is a possibility that good chips 200 are likely to be judged defective in error, which raises the fabrication cost of the chips 200.
The second problem is that the durability of the socket 210 is insufficient.
With the anisotropically conductive sheet 208 of the IC socket 210, as described above, if the deformation of the rubber material 204 is insufficient, the electrical resistance in the conductive regions of the sheet 208 does not decrease as desired. Thus, the pressure applied to the body 202 of the chip 200 needs to be large. Moreover, since the application of the pressure needs to be conducted against the elastic force of the material 204, the pressure will be rather large. In this case, the repetitive application of the large pressure to the material 204 for a long time induces plastic deformation in the material 204. As a result, the solder balls 201 are difficult to contact the material 204 as desired, which means the degradation of the socket function.
Furthermore, when such the large pressure as above is applied to the body 202 of the IC chip 200, a lot of solder waste tends to be adhered to the contact surfaces of the material 204 with the balls 201. In this case, the solder waste thus adhered to the material 204 is oxidized and accordingly, the electrical connection between the balls 201 and the regions of the sheet 208 is prevented, thereby accelerating the degradation of the socket function.
Thus, the insufficient durability will cause frequent exchange of the socket 210, which raises the testing cost.
The third problem is that the test is difficult to be carried out stably at high temperatures.
When the IC chip 200 is subjected to the so-called burn-in test, it is kept at a high-temperature atmosphere for test. At this time, the sheet 208 tends to deform (e.g., warp or bend), resulting in electrical connection failure between the chip 200 and the socket 210. This prevents desired, stable measurement.
Accordingly, an object of the present invention is to provide an IC or testing socket that ensures stable electrical connection of an IC or semiconductor device to a connection part of a test apparatus.
Another object of the present invention is to provide an IC or testing socket having a desired good durability.
Still another object of the present invention is to provide an IC or testing socket that makes it possible to conduct a desired test stably even at high temperatures.
A further object of the present invention is to provide an IC or testing socket that reduces the testing cost.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to the present invention, a socket for testing a semiconductor device with electrodes at its bottom is provided. This socket comprises:
(a) a socket body made of a rigid material; the body having penetrating openings;
(b) anisotropically conductive members formed in the respective openings of the body;
each of the anisotropically conductive members being made of an elastic material, first conductive particles dispersed in the material, and second conductive particles dispersed in the material;
the first and second conductive particles being different in average diameter from each other; and
(c) a guide for receiving a semiconductor device to be tested and guiding the device toward the conductive members in the body;
the guide being fixed to the body in such a way that electrodes of the device are contacted with the corresponding conductive members in the body.
With the socket according to the present invention, each of the anisotropically conductive members formed in the respective penetrating openings of the socket body is made of the elastic material. The first and second conductive particles are dispersed in the material, where the first and second conductive particles are different in average diameter from each other.
Thus, the first and second conductive particles are easily contacted with each other in the elastic material even if the applied pressure to the device toward the body is low. This means that electrical conductivity between the electrodes of the device and the connection part of a test apparatus is enhanced, which improves the test reliability.
Also, since the first and second conductive particles are easily contacted with each other in the material even with low applied pressure, there is no need to press strongly the electrodes of the device to the corresponding conductive members. As a result, solder waste is difficult to adhere to the surface of the conductive members. This means that the socket is scarcely affected by the defective insulation due to oxidation of the solder waste on the surface of the conductive members.
Moreover, when the conductive members are worn out, it is sufficient that only the members thus worn out are replaced with new ones.
The socket body is made of a rigid material such as metal, the socket is difficult to deform due to heat.
As described above, (i) stable electrical connection of the semiconductor device to the connection part (e.g., circuit board) of a test apparatus is ensured, (ii) a desired good durability is realized, (iii) a desired test can be conducted stably even at high temperatures, and (iv) the testing cost is reduced.
In a preferred embodiment of the invention, the socket body and the anisotropically conductive members are electrically insulated from each other by electrically insulating films formed on inner faces of the openings of the body.
In another preferred embodiment of the invention, the first particles and the second particles are approximately spherical. In this case, it is preferred that the average diameter of the first particles is in the range from 60 xcexcm to 200 xcexcm while the average diameter of the second particles is in the range from 1 xcexcm to 30 xcexcm. Within this range, the anisotropically conductive members have better anisotropic conductivity.
In still another preferred embodiment of the invention, the first particles are approximately ellipsoidal. In this case, if the ellipsoidal first particles are oriented in a direction approximately perpendicular to the electrodes of the semiconductor device. There is an additional advantage that the socket is suitable to ICs or semiconductor devices with the LGA type package that have approximately flat electrodes.
The average shorter diameter of the ellipsoidal first particles is preferably in the range from 30 xcexcm to 80 xcexcm and the average longer diameter thereof is preferably in the range from 300 xcexcm to 1000 xcexcm. The second particles are preferably approximately spherical. The average diameter of the second particles is preferably in the range from 1 xcexcm to 30 xcexcm.
It is preferred that the anisotropically conductive members are formed to protrude from a surface of the body in a space of the guide. In this case, there is an additional advantage that the contact between the conductive members and the approximately flat electrodes of the device or IC with the LGA type package is improved.
As the elastic, insulating material of the anisotropically conductive members, any elastic, insulating rubber may be used. Preferably, for example, any thermosetting resin with elasticity, such as styrene-butadiene rubber, acrylonitrile-butadiene rubber, butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, and polyurethane rubber, may be used.
In a further preferred embodiment of the invention, electrically insulting films are additionally formed on inner surfaces of the respective openings of the body. The insulating films are located between the inner surfaces of the openings and the corresponding conductive members.
As the electrically insulating films, any electrically insulating material may be used. Preferably, for example, any thermosetting resin with electrical insulation property, such as epoxy resin, polyimide resin, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, and polyurethane rubber, may be used.
As each of the first and second conductive particles of the anisotropically conductive members, any particles of any metal, such as gold (Au), nickel (Ni), silver (Ag), copper (Cu), and tungsten (W), or Au-plated Ni particles may be used.